The present invention relates to a positioning apparatus and, more particularly, to a positioning apparatus for positioning an exposure apparatus for forming a pattern on a substrate such as a semiconductor wafer or liquid crystal display panel, and to an exposure apparatus and a device manufacturing method which enable high-precision exposure by correctly holding the posture of a substrate serving as a target exposure object.
Conventionally, an exposure apparatus, such as a stepper, which projects a semiconductor device manufacturing pattern drawn on a mask or reticle onto a wafer, has a function of aligning the reticle and the wafer with each other. After the reticle and wafer are aligned with each other in accordance with this function, exposure is performed. This alignment is generally performed in the following manner. More specifically, a displacement between an original plate, such as a reticle, where a pattern to be exposed is drawn, and a target exposure object (substrate) such as a wafer is measured. Then, on the basis of the measurement result, the target exposure object is moved in a step-and-repeat manner under a control operation based on the measurement value obtained by a laser interferometric measuring machine, or the original plate and the target exposure object are moved.
A step-and-repeat type or step-and-scan type stepper must position a wafer stage, for example, which moves while holding a target exposure object (wafer), at very high precision because of its resolution and overlaying precision. In addition, in recent years, a high positioning speed is sought so that the productivity is increased.
FIG. 20 shows a model for the arrangement of a straight uniaxial positioning stage.
A stage 110 is guided on a surface plate 111 to be reciprocally movable in a straight direction. A reticle, a wafer, and other works (not shown) are placed on the stage 110. A linear motor stator (not shown) comprised of a magnet and yoke faces the stage 110 in a noncontact manner. The linear motor stator is supported by the surface plate 111. A reflecting mirror 112 is provided to the stage 110 to measure its position with a laser interferometer (not shown). Reference numeral 113 denotes a stage control system, for sending a control input command to the linear motor on the basis of a stage drive profile and the measured stage position. In practice, the stage 110 operates in the following manner. The stage 110, on which a predetermined reticle, wafer, and other works are mounted, is set in a still state. A current in a predetermined direction is supplied to a predetermined linear motor coil for a predetermined period of time in accordance with the stage position in order to accelerate the stage 110. Once the stage 110 has reached a desired speed and position, the stage control system 113 controls the stage 110 to scan it at a constant speed. While the stage 110 performs scanning, predetermined exposure, inspection, and the like are performed. After these predetermined operations are ended, a predetermined current is supplied to the linear motor coil to decelerate the stage 110 until it stops.
To achieve high-speed stage operations, the stage must be accelerated and decelerated quickly and with large magnitudes. With the above stage arrangement, operations started with acceleration and ended with positioning are performed by driving the same linear motor. If the acceleration of the stage increases, heat generated by the linear motor increases. Since the stage and the linear motor are close to each other, heat generated by the linear motor may deform the stage or work by thermal expansion, decreasing the positioning precision and exposure, machining, or inspecting precision. Heat generated by the linear motor disorders the air density of the optical path of the laser interferometer, thus degrading the measuring precision of the stage position.
It is an object of the present invention to provide a positioning apparatus having low-heat generation, high-speed, and high-precision performance.
In order to achieve the above object, according to the present invention, there is provided a positioning apparatus characterized by comprising a surface plate having a reference surface, a substage movable with respect to the surface plate, a first actuator for moving the substage with respect to the surface plate, a main stage movable with respect to the surface plate, a member for transmitting a force between the main stage and the substage, and a second actuator for positioning the main stage, wherein when accelerating/decelerating the main stage, the substage is driven by using the first actuator, to transmit a force from the substage to the main stage through the transmission member, and when causing the main stage to move at a constant speed or to stop, the main stage is positioned by using the second actuator.
The second actuator may be controlled in accordance with a time that elapses from a start time of acceleration/deceleration, or in accordance with a magnitude of acceleration/deceleration of the substage. The second actuator may be controlled in accordance with a speed of the main stage, or in accordance with a magnitude of a position deviation of the main stage.
A control system for controlling the second actuator desirably corrects a position deviation signal of the main stage with respect to a target position by using a deviation correction signal, and desirably controls the second actuator on the basis of the corrected position deviation signal. The positioning apparatus preferably has a deviation correction signal generator for generating the deviation correction signal.
The magnitude of the deviation correction signal upon a start of controlling the second actuator is desirably substantially equal to that of the position deviation correction signal obtained when the control system for controlling the second actuator starts a control operation. The gradient of the deviation correction signal upon a start of controlling the actuator is preferably substantially equal to that of the position deviation signal obtained when the control system for controlling the actuator starts the control operation.
The second actuator is desirably a noncontact actuator which generates a driving force in a noncontact manner, and is preferably a linear motor.
The movable element of the linear motor is desirably provided to the main stage, and the stator thereof is desirably provided to the surface plate. The movable element of the linear motor may be provided to the main stage, and the stator thereof may be provided to the substage.
The transmission member desirably transmits a force between the main stage and the substage in a direction along which the substage moves, and is preferably a spring element.
The transmission member is desirably a noncontact bearing which keeps the main stage and the substage apart from each other, and preferably has a static pressure bearing or a bearing utilizing magnetism.
The main stage is desirably supported on the reference surface.
The main stage is desirably placed on the substage.
The substage is desirably a two-dimensional stage movable in two-dimensional directions on the reference surface. The transmission member is preferably a radial bearing.
The main stage is desirably movable with respect to the substage in a direction parallel to the reference surface.
The positioning apparatus desirably has a driving mechanism for driving the main stage with respect to the substage in a direction perpendicular to the reference surface.
The main stage is desirably movable with respect to the substage in six axial directions.
A support mechanism for supporting the main stage with respect to the substage in a vertical direction desirably utilizes a reaction force of a pilot-pressure chamber or a repulsive force of a magnet.
In order to achieve the above object, according to the present invention, there is also provided a positioning method characterized by comprising the first acceleration step of accelerating a substage, the second acceleration step of transmitting a driving force from the substage to a main stage through a noncontact bearing provided between the substage and the main stage, thereby accelerating the main stage, and the positioning step of positioning the main stage with an actuator provided between the substage and the main stage. The positioning step further has the correction step of correcting a position deviation signal with respect to a target position, and the control step of controlling the actuator on the basis of the corrected position deviation signal.
The correction step desirably comprises generating a deviation correction signal having the same magnitude as that of the position deviation signal, and controlling the actuator on the basis of a difference in magnitude between the position deviation signal and the deviation correction signal.
The correction step desirably comprises generating a deviation correction signal having the same gradient as that of the position deviation signal, and controlling the actuator on the basis of a difference in gradient between the position deviation signal and the deviation correction signal.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.